Flashlights require stored energy to provide illumination. Flashlights contain batteries or battery packs that have one or more powered cells to provide this energy. However, at the end of a long day or shift, workers in construction, law enforcement, firefighting, military, and other fields involving heavy use of flashlights will often run their flashlight's battery power down to a level that is insufficient to provide enough light.
Rechargeable batteries have come on the market in recent years that permit batteries to be recharged during down-time. To accommodate such users, some rechargeable flashlights come with two rechargeable cells and an alkaline pack. However, even with these extra sources of power, the user must unscrew the tailcap of the flashlight, remove the discharged battery, insert a fresh battery, and then screw the tailcap back into place. The replacement operation can be difficult to perform while in the middle of a shift or a law enforcement event, or in a firefighting or military operation, particularly since it will often have to be performed in the dark, sometimes in wet, cold or otherwise-foul conditions. Moreover, the user may be wearing gloves, which can further exacerbate the problems inherent in the handling of a flashlight under adverse conditions.